The interrelationships between hearing, brain structure and function (cognition), and the ability to communicate and understand speech-in-noise remain poorly understood. Characterizing these pathways is important for understanding how interventions such as hearing aids could affect the aging brain, cognitive function, and our ability to communicate in noise. The goal of this proposal is to understand the nature of these interrelationships through conducting a brain MRI ancillary study in the Aging and Cognitive Health Evaluation in Elders (ACHIEVE) randomized controlled trial (RCT). The ACHIEVE trial (R01AG055426) is a first-in-kind RCT that will begin recruitment in 2018 of 70-84 year-old adults with mild-moderate hearing loss and normal cognition to investigate whether a hearing intervention (hearing aids, counselling, other assistive devices) versus a successful aging education control intervention reduces rates of cognitive decline. Approximately half of the n = 850 participants will be recruited from the Atherosclerosis Risk in Communities Neurocognitive Study (ARIC- NCS), a longitudinal bi-racial cohort of 15,792 adults who have been followed for >30 years. For this proposal, MRI brain scans will be conducted at baseline and 3 years later in a subset (n = 400) of ACHIEVE participants and in an additional subset (n = 200) of ARIC participants with normal hearing. By leveraging the randomized ACHIEVE study, we will have the opportunity to understand how brain structural characteristics may affect the way hearing, cognition, and hearing aid use predict speech-in-noise performance. In parallel, we will investigate how intervention with hearing aids may causally affect brain structure, thereby providing insights into potential future strategies to mitigate brain aging. The present juncture with the ACHIEVE RCT beginning active recruitment in 2018 offers a singular opportunity to incorporate brain imaging into a randomized trial that may never be repeated again on this scale in order to understand how hearing aids and brain structural characteristics interact with hearing, cognition, and speech-in-noise performance. We propose the following Aims: Aim 1 To investigate the cross-sectional associations of hearing (based on pure tone audiometry), brain MRI structural characteristics, and cognitive function with speech-in-noise performance in ACHIEVE and normal hearing ARIC participants at baseline (N = 600). Aim 2 To investigate the association of hearing aid use with improvement from unaided to aided speech-in-noise performance over 3 year follow-up and to identify which baseline factors predict the magnitude of improvement in ACHIEVE participants randomized to the hearing intervention (N = 200). Aim 3 To determine whether baseline hearing and initiation of hearing aid use are associated with changes in brain structure from baseline to 3 year follow-up (N = 600).